Sensitivity of Biogenic Emissions to Leaf Area Index and Drought

Biogenic emissions play an important role in ozone formation in the lower troposphere. Simulations of biogenic emissions for regulatory air quality modeling often use static leaf area index (LAI) values for the growing season. Our research aims to assess the value in using dynamically updated LAI from satellite data. LAI data shows significant interannual variation, which may be caused by meteorological phenomena such as drought. Because drought is correlated with high temperatures in the Southeast US, and because high temperatures also lead to increased isoprene production, there may be a contradictory feedback in isoprene emission response to severe drought. To investigate this feedback process, we have first correlated LAI to a modified Palmer Drought Severity Index compiled by Dai, as well as precipitation and temperature, for the decade 2000 to 2010. We then ran the biogenic emissions model MEGAN for two years representing wet and dry conditions over most of the country with full meteorology inputs from the WRF model. The resulting isoprene emissions estimates were then compared to LAI anomalies and drought condition in each year to find the relative impact of each. Other biogenic volatile organic compounds (BVOCs) may not respond to drought in the same way as isoprene due to less dependence on temperature and sunlight. We therefore also compared the effect of LAI and drought on other BVOCs in the same manner to see if there are differences in response that could have important implications in future regional photochemical modeling.